1. Field of the Invention
The present invention relates to a receiver for a digital modulated signal and a receiving method for the same, which receives a multi-carrier modulated signal extremely reduced in an inter-symbol interference (hereinafter referred to as ISI) or in an inter-carrier interference (hereinafter referred to as ICI).
2. Description of the Related Art
In recent years, a digital modulation method has been widely developed in a transmission of a sound signal and a video signal. In particular, a multi-carrier modulation method has attracted attention in the fact that it has a high resistance to a multi-path interference because it can expand its symbol period length. And then, an orthogonal frequency division multiplexing (OFDM) method and a modulation method derived therefrom have been actively studied.
Examples of use of OFDM include a terrestrial digital broadcasting. The OFDM is employed for the terrestrial digital broadcasting in Europe and in Japan, because of highly rating the features such that the OFDM has a high resistance to a multi-path interference and high frequency use efficiency. The OFDM is a method for modulating a plurality of carries crossing at right angles with one another by digital data to be transmitted and transmits the digital data by multiplexing those modulated waves. If the number of the carriers to be used is increased to an extent from several-hundred to several-thousand, a width of one symbol becomes extremely wide, so that the OFDM has a feature that it is hardly affected by the muti-path interference. Further, forming a transmission symbol by adding a replica of a signal at a rear section of an effective symbol in front thereof as a guard interval signal, the OFDM becomes possible to disregard the influence of the interference against a multi-path of a delay time not longer than a guard interval length. However, the existence of a multi-path interference of a delay time longer than the guard interval length causes the ISI and the ICI to deteriorate reception performance. The multi-path interference having such a long delay time presents a big problem in implementing a single frequency network (SFN).
As for a method to solve the problem, a method for canceling the multi-path interference by estimating a transmission path response by use of an adaptive equalizing filter to control a filter coefficient of the adaptive equalizing filter so as to cancel multi-path components has been designed (for instance, Jpn. Pat. Appln. KOKAI Publications No. 11-298434 and No. 2001-292120). However, if there is an estimated error in estimating the transmission path response resulting form temporal variations in noise and the transmission path response, a problem is produced such that each aforementioned conventional method cannot remove the interference components and also newly adds multi-path interference having a delay time that is integer multiple of a delay time of a delayed wave to the interference components to extremely deteriorate the reception performance.
The present invention provides a receiver for a digital modulated signal and a method for the same, which can reduce the ISI or the ICI and improve the reception performance.